1. Field of the Invention
The present invention relates to apparatuses for controlling an engine using a cam signal.
2. Description of the Related Art
Engine control units for vehicles use a crank signal whose signal level varies in a predetermined same direction at regular rotation angles (regular crank angles) of an engine crankshaft. Specifically, the crank signal is measured by a crankshaft sensor connected to an engine control unit, and the measured crank signal is input to the engine control unit operating in a main control mode.
Specifically, the engine control unit works to identify a rotational position (crank position) of the crankshaft based on the crank signal during the main control mode.
Each time it is determined that the identified rotational position of the crankshaft is matched with a desired rotational position, the engine control unit works to generate events associated with engine control, such as fuel injection or ignition during the main control mode.
Such a structure of the engine control unit described above is for example disclosed in Japanese Unexamined Patent Publication No. 2001-200747 and U.S. Pat. No. 6,445,998B1 corresponding to Japanese Unexamined Patent Publication No. 2001-214790.
In such an engine control unit using the crank signal for engine control, if the crank signal cannot be input normally to the engine control unit due to, for example, a break in wires connecting the crankshaft sensor and the engine control unit, the engine control unit cannot identify the rotational position of the crankshaft. This may cause the engine control unit not to continuously carry out proper control of the engine.
In order to address the problem, when the crank signal cannot be input normally to the engine control unit, the engine control unit is configured to operate in a sub control mode using a cam signal measured by a cam sensor. The cam signal has a level that varies in a predetermined same direction at regular rotation angles of an engine camshaft.
This allows the engine control unit to continuously generate events associated with engine control based on the cam signal during the sub control mode.
Specifically, when an occurrence of a failure in the crank signal is detected, the engine control unit is configured to switch its operation mode from the main control mode using the crank signal to the sub control mode using the cam signal so as to continuously carry out engine control. The engine control of the engine control unit in the sub control mode allows the vehicle to be driven in a limp-home mode, such as driven to a safe place slowly.
It is to be noted that the regular rotation angle of the crankshaft corresponding to a time interval between temporally adjacent signal-levels of the crank signal varying in the predetermined same direction is different from that of the camshaft corresponding to a time interval between temporally adjacent signal-levels of the cam signal varying in the predetermined same direction.
Specifically, in order to operate in the main control mode, the engine control unit requires the regular rotation angles of the crankshaft, but in order to operate in the sub control mode, it requires the regular rotation angles of the camshaft.
Accordingly, in the engine control unit, a main control system operating based on the regular rotation angles of the crankshaft and a sub control system operating based on the regular rotation angles of the camshaft may be independently constructed by hardware components and/or software components.
This may however increase hardware/software components in the engine control unit.